Electrostatic painting apparatus



July 10, 1962 F. D. WAMPLER 3,043,521

ELECTROSTATIC PAINTING APPARATUS Filed Oct. 5, 1960 2 Sheets-Sheet 1 f2 5f 76 i 56 N 76 Je W ff ifm ms ATTORNEY July 10, 1962 F. D. WAMPLER 3,043,521

ELECTROSTATIC PAINTING APPARATUS 2 Sheets-Sheet 2 Fld Oct. 5, 1960 IN VEN TOR.

fra/2A D. damp/er BY /W H15 A Y'TORNY 3,043,521 ELECTROSTATIC PAINTING APPARATUS Frank D. Wampler, Brookville, Ohio, assigner to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Oct. 5, 1960, Ser. No. 60,734

4 Claims. (Cl. 239-223) This invention relates to eelctrostatic painting apparatus and, more particularly, to apparatus for applying paint coatings of greater density and uniformity without bubbles or blemishes.

The electrostatic application of paint is used to eliminate hand spraying operations and to minimize the waste of paint and provide higher production. While the waste of paint has been reduced and higher production attained, the coating has not been as uniform as `desired and sometimes contains bubbles or blemishes.

'It is an object of this invention to provide a paint spray feed and rotatable container which will `distribute the paint more uniformly with a heavier coat upon the surface to be painted. f

It is lanother object of this invention to provide a centrifugal atornizing head inr/the form of a cup-shaped container in which no large blobs or the like are discharged by the container.

lIt is another object of this invention to provide a centrifugal atomizing head in the form of a rotatable cupshaped container in which the paint is fed in `a' uniform thin lm over the inner side walls of lche container and discharged in the desired concentrated pattern from the container onto the work in the form of uniformly fine particles of paint through the force of Ia directed electrostatic tield.

These and other objects are attained in the forml shown in the drawings in which a rotatable cup-shaped container is provided with frusto conically-shaped inner side walls diverging upwardly to a lsharp edge rim. To prevent the ilow of blobs over the side walls and off the rim of the container las it rotates at high speed, there is provided in the side walls lat the juncture With the base a recessed annular groove of relatively small capacity which receives the paint from the central distributing head and causes -any blobs or bubbles to liow into the recess along with the remainder of the liquid paint and to be held in the recess until they are dissolved. The recess is provided with a slight taper at the juncture with the side walls so as to hold lthe blobs or bubbles from flowing onto the side wall until they are dissolved. To concentrate the pattern of the electrostatically charged particles, a second annular lsharp edge rim is provided surrounding the side Walls adjacent the sharp edge rirn at the top of the side walls. This provides a second electrostatic field of the same polarity as the particles of paint which aids in shaping the pattern of the centrifugal discharged and electrostaticallyK-charged particles when an electrostatic charge is applied to the rotating cup or atomizing head.

Further objects and `advantages of the present invention will-be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the drawings: n

FIGURE l is a Sectional view of an atomizing head in the form of a rotatable cup together with the rotating means `and paint supply means; Y

FIGURE 2 is a smaller diameter atomizing head or cup for the apparatus shown in FIGURE 1; j

FIGURE 3 is an enlarged sectional view of the side wall and the juncture of the base of the container shown in FIGURE l; and

FIGURE 4 is an enlarged fragmentary sectional view ite States Patent C) Mice showing as a modified form a second outer annular sharp edge rim of larger diameter which may be applied to either of the cups shown in FIGURES 1 or 2.

Referring now more particularly to FIGURE l, there is shown an electrostatic centrifugal atomizing device in- `cluding a valve block 20 provided with a white paint supply connection 22, a color paint supply connection 24, valve controlling air supply conduit connection 26, a waste outlet connection 28 yand a thinner supply conduit 30. Normally either white or color paint from either of the supply conduits 22 and 24 will be delivered up through the hollow shaft 32 to the distributing head 34. Provi- Sion is also made for first supplying thinner to flush out the passages and then air through the supply conduit 30 to remove the thinner and paint from the passages. Provision is also made/for flow from the color paint supply 24 to the waste discharge outlet conduit 28 for removing one color paint from the block 20 before another color paint is supplied to the distributing head 34. f

The distributing head 34 receives the fluid from the shaft 32 in a central chamber 36 having 12 holes 38 extending radially outward to a conical passage 40 extending downwardly to'the `annular rim 42 of an inverted cup-shaped member 44. The passage 40 is formed between the inner frusto-conical surface ofthe inverted cupshaped member 44 and the outer frusto-conical surface of an inner member 46. The youter conical surface of the member 46 is more widely flared than the inner conical surface of the member 44 so that the tapered frustoconical passageway 40 converges as it proceeds toward the rim 42.

Rotatably mounted upon the shaft 32 is a combined .pulley and hub 50 having a pulley groove 52 receiving a belt 54 driven by a pulley 56 in turn driven by an air motor 58, all of which are located within a plastic casing 60. Clamped to the hub 50 by the gland nut 62 is the centrifugal -atomizing head in the form of a cup-shaped container 64 having a wide base portion 66 and `frusto conical upwardly diverging annular side walls 68. These cups or atomizing heads may be -made in different diameters. A smaller diameter cup is shown in FIGURE 2.

The paint under pressure issues from the frusto conicalshaped passage 40 onto the base portion 66. This is thrown by centrifugal force from the side walls 68 of the container 64. Occasionally, the diiculty has been encountered with bubbles and blobs in the paint causing blemishes when Vapplied to the Surface to be pointed. According to my invention, these blobs and bubbles are eliminated and the paint is caused to flowuniformly in a thin lm over Ithe side walls 68 by the provision of a recessed annular groove 70 in the side walls 68 at their juncture with the base 66. An enlargement of this groove is shown inFIGURE 3. This recessed groove 70 has a lower curved surface 72 of l/s radius which joins'the upper surface of the base at the bottom and which joins at the top a frusto conical surface 74 extending in the eight inch diameter cup at an angle often degrees converging upwardly. The vertical height of the groove in the eight inch size is one-quarter lof an inch. Thefrusto conical surface 74 meets the inner'frusto conical surface 76 of the side wall 68 forming a line 78 which extends around the cup.

When the cup 64 is rotating at high speed, a small reservoir of paint indicated by thereference character 80 is held in the groove 70. Thevfrusto conical surface 74 holds any bubbles, blods or globules of paint and prevents them from flowing over the line 78. They therefore are dissolved in the paint 80 in the groove 72 before they ow over the line 78 for flow in a thin film over the surfaces 76: The side walls 68 terminate in la sharp edged rim 82 for-med by undercutting the outer surface 84 of the rim at an angle of one degree so as to provide a sharp included angle of about thirteen degrees to form the sharp one terminal connected by the conductor 90 to the hollow shaft -32 through which the electrostatic charge is applied to the sharp edged container 64. The opposite terminal of the power pack 88 is `connected by the conductor 92 to the article 94 having the surface 96 to be painted. The centrifugal force causes the paint iiowing in a thin fllm over the surfaces 76 to be discharged in the form of'minute particles from the sharp edge 82 which are electrostatically charged so that they are directed by the electrostatic charge onto the surface 96 to be painted.

For the purpose of concentrating the' pattern of the paint applied, there is provided a second sharp edged rim 121'which, as shown, is threaded upon the outside of the side Wall 68. However, if desired, this rim l121 ymay be made integral with the side wall 68. A s shown, the sharp edge 123Vof this rim 121 is located one-eighth of an inch toward the base from thesharp edged -rim 82. However,

'through the provision of the threaded mounting 125, the sharp edge 123 may be moved close-r toward the rim 82 to further concentrate the pattern of spray yor it may be "moved further away to lessen the concentration of the pattern of applied paint. The 121 may be locked in place by the set screw 127 or any other suitable locking means. The ring l123 has its sharp edge formed by undercutting its outer surface 129 to an angle of ten degrees in a frusto conically shaped surface while its inner surface 131 is formed into a conically frusto shaped surface having an angle forty-ve degrees vto the -axis of the container 64. AsV shown in FIGURE 3,.the sharp edge 123V hasa diameter three-eighths of an inch geater than the diameter of the sharp edge rim 82,

However, as shown in FIGURE 4, this diameter may be increased by increasing the thickness of the rim whenever desired` For this purpose, a second rim l135 may be Vthreaded upon the threaded arrangement 125 of the container 674 as shown in FIGURE 4. This ring may similar- 4lyhave an outerundercut frusto conical surface 13-7 of ten, degrees and an inner frusto conical surface 139 of forty-tive degrees to provide an included angle of thirty-five degrees terminating in the's'harp ,edge 141 Whichmay be selected to have ya diameter greater than 'the diameter of the rim 123. For example, the rim 141 may have a diameter three-quarters of an inch greater than the diameter ofthe rim 8.2. Y

In FIGURE 2, there is shown an electrostatic atomiz- `ing head in the form of a small diameter cup-shaped container 151 which can be substituted for the cup-shaped container 64 if a smaller paint pattern is desired. This cup includes the frusto conical side walls 153 and the ,base 155, YIt is provided` with a recessed annular groove `157 inthe side Walls 153 at ,their juncture with the base 155. This lannular groove preferably has a width measr ured in the :axial direction of five-sixteenths of an inch and has a bottom curved'portion 159 of one-eighth inch radius joining the base with a -frusto-conical upper portion 161 having an angle of ten degrees to the axis and converging upwardly. The inner face 63 of the side wall r153' is in the shapeof a frusta-cone diverging upwardly --169. -If desired, the 'upper outer wall surface ,171 may be undercut at an angle of one degree.

This cup-shaped container 151 may also.' be provided with a second sharp edged rim 173 having an inner frusto conical surface 175 at an tangle of forty-live degrees and an outer frus-to-conical surface 177 at an angle of ten degrees to make a sharp edged rim 179 with an included angle of thirty-five degrees. The rim 173 is provided with .a threaded connection 181 with the side Walls 153 permitting it to be adjusted upwardly or downwardly relative to the container 151 or to be removed and another ring substituted if desired. IThe rim 179 preferably is three-eighths of an inch greater `in diameter than the rim 169 and preferably is located one-eighth of an inch closer tothe base than the rim 169.

I find that this form of container provides uniform, finely atomized paint which is deposited in a uniform manner over a concentrated paint pattern without blemishes. iBlobs of paint land bubbles are prevented by the groove lformed in the inner surface of the side wall.

While the embodiment of the present invention as herein disclosed, constitute a preferred for-m, it is to be understood that yother vforms might be adopted.

What is claimed is as follows:

1. In an electrostatic coating arrangement, a centr-ifugal -atomizing head in the form of a cup shaped container having ared side walls `and a sharp edged rim, the inner face of said side Walls being provided with a recessed Iannular paint distributing groove, said side walls being uniformly flared directly from the outer edge of said groove.

2. 1n an electrostatic coating arrangement, a centrif` i tributing groove, said groove having an inner face meeting the inner face of said side Walls, the inner face of the groove making an angle of between 5 and 15 relative to the axis of the head extending inwardly from the place `where it meets the inner face of said side walls, said side walls being uniformly ilared directly from the outer edge of said groove.

3. 'In an electrostatic coating arrangement, a centrifugal atomizing head in the form of a cup shaped container having a base and flared side walls extending from the base provided with a sharp edged rim, the inner face of the sidewalls adjacent the juncture with the base being provided with a recessed yannular paint distributing groove, said side walls being uniformly flared directly from the outer edge of said groove.

4. In an electrostatic coating arrangement, a centrifugal :atomizing head in thel fonn of a cup shaped container havingra base land flared side walls extending from the base provided with -a sharp edged rim, the inner face of the side walls adjacent the juncture with the base being provided with a recessed annular paint distributing groove, said side walls being uniformly flared directly fromthe outer edge of said groove, means for supplying paint to said base, means for rotating said head at a high speed for centri-fuging said paint into said groove and for causing the paint to flow -in a uniform thin lm out of the groove over the flared side walls for centrifugal `dis-l charge from said sharp edged rim.

References Cited in the tile of this patent LFoster May 30. 1961 

